Knee arthroplasty is a well-known surgical procedure wherein a diseased and/or damaged natural knee joint is replaced by a prosthetic knee joint. A typical knee prosthesis may include a tibial component, a femoral component, and a patellar component. The femoral component generally includes a femoral stem and a pair of spaced-apart condylar portions, the superior surfaces of which articulate with a portion of the tibial component. The femoral stem seats within the medullary canal of a resected femur. Similarly, the tibial component includes a stem implantable into a resected tibia, the stem being secured to a tibial plateau that faces the condylar portions of the femoral component.
As normal anatomical variations preclude the use of a standard size or type of any of the above components, modular prosthetic knees have been developed that allow for limited adaptation or exchange of one or more components to provide a customized prosthesis. With respect to the femoral component, for example, it is known to provide a selection of variously angled and sized femoral stems that are attachable to the remainder of the femoral component with a screw. In practice, the femoral stem is rotated with respect to the femoral component and screw until the femoral stem is tightly bound against a surface of the femoral component and cannot be further rotated. Such a configuration is generally acceptable for a cylindrical, nonangled femoral stem because the radial position at which the femoral stem binds has no effect on the orientation of the femoral stem.
By contrast with a cylindrical femoral stem, a femoral stem having a flattened portion that must be inserted into the medullary canal at a particular orientation or a femoral stem that must be laterally angled with respect to the remainder of the femoral component, the radial stopping point or positioning of the femoral stem is critical. However, it is quite difficult to screw the femoral stem in place and ensure that the femoral stem binds against the femoral component at a predetermined radial point. Additionally, a wide selection of relatively expensive femoral stems must be stocked.
In addition to lateral offset, the size, shape, or condition of a patient's femur sometimes requires that the femoral stem be offset from a central location in either an anterior or posterior direction. Flexible or easily adjusted anterior-posterior offset is not provided by known prostheses. Similar considerations and problems apply to the tibial component.